1. Field Of The Invention
The present invention relates to an insufflation cannula assembly adapted to receive a trocar, endoscope or other surgical instrument and for use in conjunction with insufflatory surgical techniques, and more particularly relates to a valve used in the assembly for maintaining insufflation pressure in a body cavity.
2. Description Of The Prior Art
Insufflatory surgery involves filling a body cavity with a pressurized gas to maintain the cavity under a certain predetermined pressure. One way of performing the surgery is by first puncturing the skin in a desired body cavity region with a needle. The needle includes a stylet which introduces an insufflation gas into the body cavity to inflate it.
A trocar is then used to puncture the body cavity. The trocar is inserted through a cannula or sheath, which cannula partially enters the body cavity through the incision made by the trocar. The trocar may then be removed from the cannula, and an elongated endoscope may be inserted through the cannula to view the anatomical cavity.
Various types of cannula or trocar assemblies are provided with valves for maintaining a certain gas pressure in the cavity when the trocar or other surgical instrument is removed from the cannula.
For example, U.S. Pat. No. 4,654,030, which issued to Frederic Moll et al., and copending U.S. application Ser. No. 920,509, filed Oct. 17, 1986, disclose a trocar assembly having a cannula and employing a flapper valve to close off the cannula passage after the trocar or other instrument has been withdrawn.
As shown in FIG. 7 of the Moll et al. patent, the flapper valve includes a U-shaped flapper 82 and a grommet 77 formed with a central opening 78 through which the trocar may be inserted or withdrawn. The flapper carries a circular pad 87, and is spring-biased so that the pad engages grommet 77 and forms a seal with the grommet.
Although the flapper valve disclosed in the Moll et al. patent works well in most applications to maintain pressure in the body cavity, there are certain inherent drawbacks in its design.
First, the circular pad is rigidly mounted on the flapper so that it cannot move with respect to the flapper. If the pad and grommet are slightly out of alignment when the valve closes, the pad may not seat properly on the grommet, and insufflating gas may leak from the body cavity through the valve.
Second, the circular pad is made of a deformable material such as Tygon (TM), and is formed by a molding process. Irregularities in the pad's grommet-engaging surface due to shrinkage of the pad material during its formation may provide leakage paths through the valve. Also, the pad bears with considerable spring pressure on the side of the trocar when the trocar is inserted into the cannula through the valve. A depression may form in the pad's surface which may cause further leakage when the valve closes.
Third, the circular pad is relatively flat or has a slight curvature. It engages protruding lips 88 formed on the grommet, which lips surround the grommet opening 78. With this structure, the flapper valve disclosed in the Moll et al. patent provides minimal contact area between the pad and the grommet, and any slight irregularity in one or the other may cause the valve to leak.